# Autotune yes or no

It always comes back to the question whether Autotune is good or not?

Personally and for our lab in particular no. We “hand” tune for max deflection at approach speed. Min speed just above stall. Max at something reasonable for that aircraft. Scaling speed get set to approach speed. Then we put a blower on the pitot tube and give it the approach speed while moving the plane around to set max deflection at approach speed. We have usually already done a stability and control analysis as Nelson describes in his book for the aircraft.

What do you mean by this? Also are you able to describe the process a little but with regards to the moving the aeroplane around when you have the blower on the pitot. Sounds interesting…

Aircraft usually have a target landing speed and a target approach speed. Usually control surfaces are sized for max deflection/rate for TO/L.

http://ardupilot.org/plane/docs/parameters.html#scaling-speed-speed-used-for-speed-scaling-calculations

Scaling speed is where the PID control are scaled to 1. The rest of the math behind it can be found in the source code. I don’t think there is a documentation page for that yet. The code uses it’s best guess for airspeed when calculating how much to scale the PID values. So a pitot tube gives it an airspeed and the output scaled PID can be seen through the control surfaces. Max theta command in FBWA should give max elevator deflection and flipping back to manual should not move the control surface. Also when the aircraft is moved to match the theta input the control surface should go back to the trim point after the integrator has had time to work out to zero.

One other thing. The 30deg/45deg for the INT_LIMIT is WAY TOO BIG. That means 2/3 of the deflection of the control surface can use used for trimming the aircraft. That’s just ludicrous and should be changed for anyone that knows how to trim an aircraft.

Thanks for the info! Step 1 will be to get the PIDs accurate and then finesse with the scaling. Do you have any tips for the manual tuning aside from what is already in the wiki?

We usually get everything trimmed out in a few manual flights. We already had procedures for trimming before using the ArduPilot system.